1. Field of the Invention
Networks and methods consistent with the present invention relate generally to an ad-hoc network and a routing method thereof, and more particularly, to an ad-hoc network for discovering the most stable route to transmit data from a source node to a destination node and vice versa in consideration of the mobility of nodes establishing the ad-hoc network.
2. Description of the Related Art
A typical mobile communication system transmits data between a mobile element and a base station. The mobile element and the base station transfer data directly to each other without passing through other mobile elements or nodes. By contrast, in an ad-hoc network data may be transferred from a source node to a destination node, and the data can be relayed via other nodes placed between the source node and the destination node.
A construction of a conventional ad-hoc network is explained below in reference to FIG. 1. As shown in FIG. 1, the ad-hoc network includes a source node 100 and a plurality of nodes 110. Although only one source node is illustrated in FIG. 1, more source nodes can be included in the ad-hoc network.
A source node transmits data destined for a destination node. The destination node receives the data from the source node. If the source node is placed within a specified distance from the destination node, the data is directly delivered to the destination node. However, if the source node is beyond the specified distance, the source node cannot transmit the data directly to the destination node. Accordingly, in this situation, the source node forwards the data to neighbor nodes adjacent to the destination node, rather than transferring the data directly to the destination node. As stated above, a node beyond a specified distance transmits data via neighbor nodes in order to minimize the power consumption required for the data transmission. The transmission power is proportional to the distance between the source node and the destination node. Accordingly, a source node, which lies beyond a specified distance from a destination node, transmits the data via the plurality of the nodes and thus minimizes the power consumption for the data transmission.
FIG. 2 illustrates a routing method in an ad-hoc network. The method for routing the data from a source node to the destination node is explained in detail below in reference to FIG. 2. It should be noted that the following method description uses Routing REQuest (RREQ) messages and Routing REPly (RREP) messages to communicate between nodes; however, any type of message known in the art is contemplated and may be used.
The source node A generates a RREQ message containing its location information and location information of the destination node D. The source node broadcasts the generated RREQ message to its neighbor nodes B and C. As shown in FIG. 2, nodes B and C receive the broadcast RREQ message. Upon receiving the RREQ message, the nodes B and C compare their addresses with the destination address contained in the RREQ message. When the destination address does not match their addresses, the nodes B and C update and broadcast the received RREQ message to their neighbor nodes. The updated information includes a hop count.
The RREQ message broadcast from the source node A finally arrives at the destination node D along paths. The destination node determines it is the destination of the RREQ message when the destination address contained in the received RREQ message matches its address. Next, the destination node selects a path having the smallest hop count of hop counts contained in the received RREQ message. That is, the destination node D selects the route having the hop count of 2 which passes through the node B. The destination node D transmits to the source node a RREP message containing the information as to the selected path having the smallest hop count. The source node selects as the route to the destination node the path having the smallest hop count contained in the received RREP message. The source node transmits the data to the destination node along the selected route by way of the node B.
As such, the source node establishes the route and transmits data to the destination node. However, due to the node mobility, radio properties, etc the established route is temporary. In this regard, a routing method in consideration of the mobility of the nodes would be desirable.
A conventional method for taking account of the mobility of nodes adopts the random waypoint model (RWP), but the RWP model is inapplicable to real-time routing protocols under actual network environments. The other methods that exist reflecting the mobility of nodes assume that every node moves rectilinearly with uniform velocity so as to simplify the mobility modeling. However, these methods are problematic because nodes in the ad-hoc network move freely and irregularly with irregular velocity. Hence, it is impossible to predict the mobility of nodes and to establish a stable route in consideration of the irregular mobility of the nodes over actual ad-hoc networks using conventional methods. In the event that a node placed along the established route moves and deviates from the route, it takes a long time to re-establish a route. In addition, it is infeasible to transmit real-time data during the route re-establishment.